This invention relates to a photogrammetric plotting apparatus of the kind having means for moving two stereographic plates in their plane with respect to two optical systems so as to bring corresponding regions of the two plates into the optical axes or the lines of sight of the two optical systems, and means for indicating, by a reference mark, the trace of the line of sight on each plate, the plotting apparatus also comprising a permanently-located plate-observing device.
The invention relates more particularly, as its most promising though not exclusive application, to photogrammetric plotting devices in which the motion of the stereographic plates is controlled by analytical computing means.